1. Field of the Invention
The present invention relates to a novel process for preparing a coated product by electrodeposition of a water-dispersion varnish.
2. Description of the Prior Art
Heretofore, it has been well-known to use electrodeposition for the formation of a cured synthetic resin film onto a conductive substrate. There are two such processes: electrodeposition of a water soluble varnish and electrodeposition of a water dispersion varnish. In the former process, the substrate is conductive and is the anode for deposition of the water soluble varnish. The deposited layer usually has insulating properties. Accordingly, the thickness of the electrodeposited layer is limited and the process is not suitable for the preparation of a cured synthetic resin coated insulation product. On the other hand, in the latter process for electrodeposition, the substrate is again the anode but the deposition is of a water-dispersion varnish. The material in the layer is deposited in the form of particles with spaces in between whereby the conductive substrate is not insulated, allowing an increase in thickness of the deposited layer. When the layer deposited in the water-dispersion varnish case is cured, many of the particles in the deposited layer will be adhered to each other. However, it is difficult to form a continuous film which is free of cracks and imperfections. In order to overcome these disadvantages, it has been proposed to treat the coating with a hydrophilic organic solvent following the electrodeposition (Japanese Patent Publication No. 31555/1970). It has been also proposed to place a coating of an insulation varnish after the electrodeposition of the water-dispersion varnish (Japanese Patent Publication No. 51096/1972), and to electrodeposit a water soluble varnish after the electrodeposition of a water-dispersion varnish (Japanese Patent Publication Nos. 5247/1973; 9456/1973 and 43708/1973). Another proposed solution is contained in Japanese Patent Publication No. 4604/1973.
In the conventional processes, various film forming auxiliary agents have been applied. In general, the film forming auxiliary agent produces a toxic solvent gas during the curing operation. Accordingly, it has been undesirable to discharge the solvent gas into the air. This is also unwarranted from the viewpoint of loss of solvent. It is, therefore, necessary to have additional solvent recovery equipment, although the processes so far proposed, e.g., Japanese Patent Publication No. 31555/1970, do contain somewhat favorable features which enable simple and effective solvent recovery. When an insulation layer having a thickness of more than 100.mu.m is formed by electrodeposition, it has been necessary to apply a curing step or a heat curing step by elevation of temperature after treating the coated layer with the film forming auxiliary agent, whereby the curing operation becomes complicated.
In general, in the past, an insulation varnish coated wire has been prepared by either of the following processes. A bare wire is dipped into a varnish tank and the amount of coated varnish is controlled to a desired amount by passage through a floating die, etc. The coated wire is then cured. These steps are repeated several times to form a coated film having the desired thickness. Alternatively, a water soluble or water-dispersion synthetic resin varnish is deposited onto a conductive wire by electrophoresis to form a coated film having uniform thickness. In the latter case, the process has been advantageously easy. However, it has been difficult to obtain a continuous film having high insulation intensity using the conventional electrodeposition processes. Accordingly, it has been necessary to use a film forming auxiliary agent in order to obtain a continuous film having high insulation intensity using electrodeposition with a water-dispersion varnish. It has been necessary to apply a water washing tank and a post-treatment tank between the electrodeposition equipment used to deposit water-dispersion varnish onto the conductive wire and the curing equipment.
Additionally, it has been known to coagulate deposited latex particles by electrodepositing a water-dispersion varnish and boiling the coated layer. However, it has been difficult to obtain a smooth surface. Also, the process has not been suitable for preparing a coated wire by the electrodeposition of water dispersion varnish. An insulation coated wire to be used for a magnet coil is generally coated with grease in order to enable smooth winding. Since the smoothness of the coated film has a close relationship with the appearance, the existence of pin holes in the coated film, the abrasion resistance, the flexibility and the durability of the wire, any process producing an unsmooth product is inapplicable.
It would be most desirable to have a process for producing an insulating coating which is free from the aforementioned disadvantages.